Is it certain that Raymond Smullyan invented this type of puzzle? I first came across it in the early sixties, and it was old then.

It's known that Smullyan invented the "knights and knaves" scenario, in order to avoid the Unfortunate Implications of the original "two primitive tribes" scenario, along with the variations involving insanity and vampirism (but not the "me no speak English" variant), but the puzzle itself probably goes back to Lewis Carroll's time.

The earliest mention I've been able to find is a letter by the computer scientist John Mc Carthy in Scientific American in 1957. Mc Carthy gives the "da" and "bal" variant (he uses "pish" and "tush"), but he writes as if the original problem was well-known by then.

Smullyan was born in 1919, so it's possible that he invented the puzzle in time for it to be well-known by 1957, but not very likely.

Lewis Carroll wrote at least one fairly similar puzzle in 1895: the Five Liars. Five people - A,B,C,D,E - each make two statements, of the form "Either B or D tells a Truth and a Lie; either C or E tells two Lies". A few years later, he wrote to his friend Professor Wilson "I hope you will be pleased to know I have decided to abandon my 'Liar' Problems; the metaphysical difficulties are too appaling!", which suggests that sort of puzzle was not common, and maybe was invented by him.

Vilui

04:55:03 PM May 13th 2010

Yes, I'm going to remove the ridiculous claim that Smullyan invented this type of puzzle from the page. As well as the above facts, Martin Gardner was a friend of Smullyan and would certainly have credited him if he had invented it.

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